Yeah, that could work too. You should definitely have the digital volume for the Asgard set to 100%, and control volume using the knob. Digital volume will (theoretically at least) reduce sound quality by lowering the bit-depth of the signal.
For burn-in, I just set my music library to random, turn the volume up a little more than normal, and let everything play constantly for a few days. But don't get too hung up on burn-in -- you can listen to the equipment, and enjoy it, during the process. I've seen some people who don't even want to listen until everything is "done" burning in, which is ridiculous IMO. There is some debate about how much burn-in matters, if at all. Headphone and DAC burn-in is a bit contentious, but tubes definitely need to burn in -- there is a substance inside the glass that helps to create the vacuum, and it needs to be heated up to start working and create a full vacuum. As for headphones and DACs, maybe burn-in makes a difference, maybe not, but the only harm that can be done is to deprive yourself of listening to your gear while you wait for the process to finish.
EDIT -- Oops, I was thinking of Valhalla. Asgard doesn't have tubes.
Edited by manbear - 1/13/14 at 8:39pm